Mechanized units are known that are moved through a trench in the ground for the purpose of laying a continuous length or connected lengths of a utility or utilities, such as conduits, pipes, cables, etc. or combinations thereof. The mechanized unit is primarily intended to place in the trench flexible utilities such as electrical and communication and data cables or rigid pipes for water, sewer, and/or gas, or any combination thereof, and then encase the one or more utilities with protective material. The mechanized unit may be propelled through the trench by being connected directly to the device that excavates the trench or by any other mechanical moving device, such as a tractor or other vehicle.
In one type of application, the flexible utility or utilities pass down through the unit onto the bottom of the trench by means of a guide device that maintains a desired spatial relationship between utilities in applications in which more than one utility is laid in the trench. As the utility or utilities pass through and/or exit the guide device, protective material, which has been deposited in the upper portion of the mechanized unit, gravitates in a generally vertical direction through the mechanized unit, onto and around the utility or utilities being installed. This type of installation has a disadvantage in that the material to be used for the encasement must be specially obtained, usually by purchasing, from a suitable processing facility, such as a gravel/sand pit or stone quarry. Alternatively, the encasement material must be processed on site using portable screening equipment. The purchasing, hauling and handling or processing and handling of this protective material can add considerable time and costs to the installation.
U.S. Pat. No. 6,981,342, which is assigned to the assignee of the subject application and whose disclosure is incorporated herein in its entirety by reference, describes a mechanized unit that overcomes the forgoing disadvantages in an application that uses excavated trench material and that protects the utility or utilities in a trench in a manner that is efficient and cost effective.
In accordance with the invention of the aforesaid patent, a mechanized unit is provided that places a continuous length or connected lengths of a utility or utilities at a predetermined spatial relationship with each other near the bottom of an excavated trench. As the mechanized unit moves along the trench, it sweeps the excavated material that has been placed along the one or both sides of the trench back into the trench onto a screening member. The screening member is constructed with vertically separate layers of screening material with the screen layers from top to bottom having progressively smaller openings. The screening member is mounted to the unit with a downward slope from the front to the back in the direction of unit movement. As the unit moves, layers of the excavated material of increasing particle size are deposited over the utility or utilities one layer above the other. The layer of smallest particles directly encase the utility or utilities rather than larger size particles. This protects the utility or utilities from stresses or direct physical damage that would be caused by large excavated soil or rock particles. The successive upper layer or layers further protect the utility. The mechanized unit of the invention accomplishes this in one continuous operation together with the laying of the one or more utilities.
The mechanized unit of the patent is provided with vertical side walls that hold back the sides of the trench. This prevents collapse of the trench walls and also prevents any material from falling into the trench which could damage the utility or utilities being installed prior to their encasement by the protective screened material.